While anestetizing patients anesthetic agent is typically held in a vessel having a liquid space and a gas space in which vessel the agent is vaporized into a carrying gas, which may require heating depending on physical features of the agent. Vaporized anesthetic agent mixed with the carrying gas is then led to a patient for inspiration. However, vaporizers like these are producing vapor continuously and not at times when the vapor is useful to feed to a patient. Also it takes a lot of room which is limited in operating rooms where these devices are used.
Another type of vaporizer is also known where anesthetic agent is supplied from a liquid reservoir to a piezoelectric pump which is capable of generating liquid droplets into an inspiration of a patient. However, this kind of pump causes difficulties while cleaning it after any use. Especially there is a heating element in an airway leading to a patient which is very difficult to clean. Some cleaning devices may even break the device. The whole unit should be sterilized before using it with another patient. Anesthetic agents may dissolve glue joints needed in this structure to fix piezoelectric element to other structure surrounding. Anesthetic agents further have very low surface tension which means that it does not behave like many common nebulized agents and thus it is expected anesthetic agents may cause problems with this kind of products.
Further various technologies used with nebulizers to deliver atomized medicine to a patient are known. For instance it is well-known to use a thin mesh plate having holes and which plate is vibrated at ultrasonic frequencies to cause a liquid to pass through the holes to atomize the liquid. Vibration may be produced by measuring current, voltage or phase angle taken by the element or by measuring the resistance of the strain gauge attached to vibrator. As the vibrating element there is typically used a piezoelectric element adjacent an upper surface of the mesh plate to vibrate this plate. The piezoelectric element is spaced from the mesh plate by a small gap and secured to it about its periphery e.g. by conductive glue, brazing, welding which may be damaged by anesthetic agents. There is a sensor to measure liquid supplied to the surface of the mesh plate and this is automatically controlled to maintain a desired volume of liquid on the surface of a mesh plate. Or alternatively there are two plates spaced from each other so that a volume is defined between them and these plates are formed to establish a mutual capacitance reflecting the amount of liquid in the volume. The measured capacitance reflects the amount of liquid in the nebulizer which information can be used to control the supply of liquid into the volume and through the holes of one of the plates. Again cleaning is a problem when the unit is reused with another patient especially because it is one compact unit. Also in this case especially anesthetic agents dissolve glue joints of the structure. Further measurement of electrical conductivity of anesthetic agents cannot be exploited in this nebulizer, because anesthetic agents are insulants. Anesthetic agents have very low surface tension which means that it does not behave like many common nebulized agents and thus it is expected anesthetic agents may cause problems with this kind of products.
There are also nebulizers having a structure where a vibrator is arranged opposite to holes of a detachable mesh member pushing a liquid directly through the holes. A longitudinal movement of the vibrator away from the mesh member causes a suction effect to a reservoir whereupon the liquid starts to flow to a volume between the holes of the mesh member and the vibrator and when the vibrator is moving towards the member the liquid is pushed through the holes forming small droplets for a patient breathing. Thus atomization of liquid is not achieved by a vibration of the membrane but the oscillator itself is pushing the liquid. Especially this does not work with anesthetic agents if there is no active dosing system for the liquid. The surface tension of anesthetic agents is so low that agents flow from the reservoir to the member and are able to escape through those holes, too. Also a production of droplets ceases if the member's output surface is getting wet, which happens from time to time.